U.S. Pat. No. 6,079,821 issued to Chwalek et al. discloses a continuous ink jet printhead in which deflection of selected droplets is accomplished by asymmetric heating of the jet exiting the orifice.
U.S. Pat. No. 6,554,410 by Jeanmaire et al. teaches an improved method of deflecting the selected droplets. This method involves breaking up each jet into small and large drops and creating an air or gas cross flow relative to the direction of the flight of the drops that causes the small drops to deflect into a gutter or ink catcher while the large ones bypass it and land on the medium to write the desired image or the reverse, that is, the large drops are caught by the gutter and the small ones reach the medium.
U.S. Pat. No. 6,450,619 to Anagnostopoulos et al. discloses a method of fabricating nozzle plates, using CMOS and MEMS technologies which can be used in the above printhead. Further, in U.S. Pat. No. 6,663,221, issued to Anagnostopoulos et al., methods are disclosed of fabricating page wide nozzle plates, whereby page wide means nozzle plates that are about 4″ long and longer. A nozzle plate, as defined here, consists of an array of nozzles and each nozzle has an exit orifice around which, and in close proximity, is a heater. Logic circuits addressing each heater and drivers to provide current to the heater may be located on the same substrate as the heater or may be external to it.
For a complete continuous ink jet printhead, besides the nozzle plate and its associated electronics, a means to deflect the selected droplets is required, an ink gutter or catcher to collect the unselected droplets, an ink recirculation or disposal system, various air and ink filters, ink and air supply means and other mounting and aligning hardware are needed.
In these continuous ink jet printheads the nozzles in the nozzle plates are arranged in a straight line, they are between about 150 to 2400 per inch and, depending on the exit orifice diameter, can produce droplets as large as about 100 Pico liters and as small as 1 Pico liter.
As already mentioned, all continuous ink jet printheads, including those that depend on electrostatic deflection of the selected droplets (see for example U.S. Pat. No. 5,475,409 issued to Simon et al), an ink gutter or catcher 10 is needed to collect the unselected droplets. Such a gutter has to be carefully aligned relative to the nozzle array since the angular separation between the selected and unselected droplets is, typically, only a few degrees. The alignment process is typically a very laborious procedure and increases substantially the cost of the printhead. The printhead cost is also increased because each gutter must be aligned to its corresponding nozzle plate individually and one at a time.
The gutter or catcher may contain a knife-edge or some other type of edge to collect the unselected droplets, and that edge has to be straight to within a few tens of microns from one end to the other. Gutters are typically made of materials that are different from the nozzle plate and as such they have different thermal coefficients of expansion so that if the ambient temperature changes the gutter and nozzle array can be in enough misalignment to cause the printhead to fail. Since the gutter is typically attached to some frame using alignment screws, the alignment can be lost if the printhead assembly is subjected to shock as can happen during shipment. If the gutter is attached to the frame using an adhesive, misalignment can occur during the curing of the glue as it hardens, resulting in yield loss of printheads during their assembly.
These problems of alignment and assembly are exacerbated as the printhead lengths are increased from an inch or less to page wide which could be tens of inches long.
A need therefore exists for an assembly free and self-aligned ink gutter or catcher for page wide nozzle arrays that is free of misalignment due to changes in the ambient or operating temperature. Furthermore, a need exists for an ink gutter or catcher that is assembly free and self aligned to smaller nozzle arrays, which may then be arranged in a staggered or tiled configuration to form page wide continuous ink jet printheads. Finally, a need exists to reduce the cost of the printheads by eliminating the labor-intensive alignment procedure and the one at a time alignment process of each nozzle plate to its corresponding gutter.